The present invention relates to declutching devices, especially to devices for disengaging friction clutches of motor vehicles. More particularly, the invention relates to improvements in declutching devices of the type wherein the disengaging unit comprises a sleeve which is movable along an elongated guide and carries an antifriction bearing one race of which can be moved into engagement with the prongs of a diaphragm spring in the friction clutch of a motor vehicle or the like.
It is known to provide the sleeve of the disengaging unit with two motion receiving portions which are disposed diametrically opposite each other and can be engaged by the arms of a bifurcated actuating member in the form of a fork. The arms straddle the guide for the sleeve and are pivoted into motion transmitting engagement with the respective motion receiving portions of the sleeve in order to shift the latter longitudinally of the guide. The sleeve is mounted on the guide for axial movement with a minimum of play and the guide is normally an elongated cylindrical pipe or tube which surrounds the input shaft of the change-speed transmission of the motor vehicle. When the clutch is engaged, it transmits torque from the crankshaft of the engine to the input shaft of the transmission. In order to disengage the clutch, the sleeve is moved axially of the guide by the pivoting arms of the actuating fork to thereby deform the diaphragm spring of the clutch with the result that the pressure plates are disengaged from the friction linings on the clutch disc which latter receives torque from the crankshaft.
The arms of the fork are normally mounted for pivotal movement about a fixed axis. In many motor vehicles, the fixed pivot axis for the fork extends at right angles to the axis of the reciprocable sleeve and is defined by a shaft which is journalled in the case of the change-speed transmission. In such declutching devices, the wear upon the sleeve and/or fork is quite pronounced, especially because the sleeve is often engaged and shifted by a single arm of the fork. This is due to unavoidable machining tolerances, not only as regards the making of the fork but also as concerns the treatment of those portions of the sleeve which receive or are supposed to receive motion from the arms. If one of the arms is twisted or otherwise deformed, it is likely to engage the corresponding motion receiving portion of the sleeve ahead of the other arm which latter is then held out of contact with the associated motion receiving portion. Consequently, the sleeve is likely to jam or to offer a very pronounced resistance to axial movement along its guide. The just discussed phenomena will develop in the majority of disengaging or declutching devices, i.e., it is rather infrequent that both arms of the fork engage the respective motion receiving portions of the sleeve at the same instant and to the same extent. Pronounced frictional engagement between the sleeve and its guide is undesirable because it adversely affects the disengaging operation and also because the return movement of the sleeve to its starting position is equally unpredictable. Moreover, the useful life of the sleeve and/or guide is short, especially if the sleeve is made of a synthetic plastic material. The same applies when the component parts of the declutching device are mass-produced elements consisting of sheet metal or the like.
In order to compensate for manufacturing tolerances and/or for deformation of the fork and/or sleeve subsequent to assembly, it was already proposed to provide an insert between each arm of the fork and the respective motion receiving portion of the sleeve and to secure the inserts to the associated arms by way of elastic clamps. Each insert further comprises a relatively narrow web which abuts against the non-rotating race of the antifriction bearing on the sleeve at a position which is angularly offset by approximately 90 degrees relative to the corresponding elastic clip. The inserts are free to pivot about their respective webs to compensate for manufacturing tolerances and to thus ensure the application of force to both motion receiving portions of the sleeve.
A drawback of such declutching devices is that the inserts constitute additional component parts which contribute to initial cost of the declutching devices. Moreover, installation of such inserts in the declutching devices is time consuming and the cost of inserts is rather high.